Recent advancements in wireless communications require an RF receiver that can support a wide dynamic range of analog input signals. A digital step attenuator (DSA) is widely used in the RF receivers with wideband and multiband applications. The DSA is an analog attenuator whose attenuation is controlled digitally. The DSA can be integrated with the RF receiver or it can be external to the RF receiver. However, it is preferred to integrate the DSA in the RF receiver since it reduces the overall board area and also the cost.
Due to high dynamic range of analog input signals received by the RF receiver, the DSA is required to support a large range of attenuations. This ensures that a voltage level reaching the other components of the RF receiver post DSA is within a defined limit, so as to ensure normal operation of the RF receiver. Thus, DSA is important for ensuring reliability of the components used in the RF receiver. An effective resistance at an output of the DSA should be large to get a good noise figure. One major drawback of having large effective resistance is the slow transient settling that occurs whenever an attenuation of the DSA is modified.